Overhead cranes such as, for example, gantry and industrial cranes, are generally known for lifting heavy items weighing up to several hundred tons. Such cranes are often used for handling large products or containers and transporting them between storage locations and transportation such as ships, trains, trucks, etc. These cranes are commonly used in the construction industry as well, handling large construction materials, such as beams, blocks, concrete barriers, pipeline sections, prefabricated components, etc.
Conventional overhead cranes usually include two parallel horizontal beams that are elevated above a support (e.g., a frame made of horizontal and vertical members). Each of these horizontal beams is equipped with a trolley that is movable along the horizontal beam. Furthermore, each trolley includes a hoist for lifting and lowering a load. The hoist includes a cable, which depends downwardly from the trolley, and a hook block or the like that is suspended by the cable. For moving the entire crane, the support frame may include drivable and steerable wheels so that an operator can drive the crane over a job site to lift a load at one location and to deposit the load at a desired location.
In an attempt to ensure safety of site workers, prevent damage to a load being hoisted by the crane, and prevent damage to the crane itself (e.g., structural members, hydraulics, etc.), some cranes can be driven only at one relatively slow speed. However, such a configuration can be inefficient, particularly because a time to travel between two locations when the crane is in a loaded state (i.e., hoisting a load) is, disadvantageously, the same as a time to travel between two locations when the crane is in an unloaded state. Similarly, the trolleys and hoists of such foregoing cranes can only be operated, disadvantageously, at one speed. Thus, it takes an operator the same amount of time to raise the hoist and move the trolley when loaded as it does to raise the hoist and move the trolley when unloaded.
In an attempt to overcome these disadvantages, some cranes have been provided with a manually-operated control switch for varying the driving speed of the crane between a slow speed and a fast speed. However, as one can appreciate, a speed control of this sort is not ideal in some instances, for example, when the operator fails to select an optimal speed setting.
In view of the foregoing, a need exists for an improved control system and method for operating a crane.